The goals of this application are: to contribute to the body of knowledge on the role of hearing in speech production; to describe the speech of hearing-impaired persons and the effects of prostheses; and to evaluate and refine the properties of a model of the role of hearing in speech. We pursue those goals by conducting experiments with: adult cochlear implant users; hearing aid users; deaf speakers who do not use prostheses; and speakers with normal hearing. According to our model of the role of hearing in adult speech motor control, speech production involves auditory goals and thus mappings between articulatory movements and their auditory consequences. The project investigates: (1) how mappings are degraded after long deafness, retuned when some hearing is restored, and affected by short-term changes in hearing; (2) the effects on speech when bite blocks are introduced with and without hearing; (3) evidence that the mapping of allophonic variation into auditory goals improves after the speaker receives a cochlear prosthesis; (4) the structure of phonetic categories in prosthesis users; (5) the effects of increasing the number of auditory goals (by comparing two languages with different vowel inventories) on responses to changes in auditory feedback; (6) the effects of clarity demands and auditory feedback on phonetic contrasts; (7) the timing of changes in speech parameters in response to changes in hearing; (8) effects of hearing status on audio-visual integration of spoken syllables; (9) effects of hearing loss on activation of auditory cortex by visible speech; (10) effects of age at hearing loss on cortical activation during speech; and (11) the effects of age at hearing loss on phonetic contrasts. Independent variables that are employed in most of the studies are: initial provision of a cochlear implant; modification of auditory feedback; and the stage at which the modification is made (before implantation, shortly after, long after). In general, the effects of these interventions are assessed by examining phoneme recognition, levels of cortical activation and, in speech production, acoustic measures of selected phonetic contrasts - consonantal and vocalic - as well as properties of the overall acoustic vowel space.